[PATCH v1 06/12] gpu: nova-core: mm: Add Pfn (Physical Frame Number) type

[Joel Fernandes <joelagnelf@nvidia.com>]

Add the `Pfn` (Physical Frame Number) type representing a physical page
in VRAM, along with the macros used by frame-number types to interop with
the `Bounded<u64, N>` representation used by bitfield-derived PTE/PDE
fields.

In later patches in the series, we will use `Pfn` in the page table
structures.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
 drivers/gpu/nova-core/mm.rs | 70 +++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 drivers/gpu/nova-core/mm.rs

diff --git a/drivers/gpu/nova-core/mm.rs b/drivers/gpu/nova-core/mm.rs
new file mode 100644
index 000000000000..3b131aedf2f9
--- /dev/null
+++ b/drivers/gpu/nova-core/mm.rs
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Memory management subsystems for nova-core.
+
+#![expect(dead_code)]
+
+/// Implements `From` conversions between a frame-number type and `Bounded<u64, N>`.
+///
+/// Each MMU version module should invoke this for the specific bit widths used by that version's
+/// PTE/PDE bitfield definitions.
+macro_rules! impl_frame_number_bounded {
+    ($type:ty, $bits:literal) => {
+        impl From<Bounded<u64, $bits>> for $type {
+            fn from(val: Bounded<u64, $bits>) -> Self {
+                Self::new(val.get())
+            }
+        }
+
+        impl From<$type> for Bounded<u64, $bits> {
+            fn from(v: $type) -> Self {
+                Bounded::from_expr(v.raw() & ::kernel::bits::genmask_u64(0..=($bits - 1)))
+            }
+        }
+    };
+}
+
+/// Implements `From` conversions between [`Pfn`] and `Bounded<u64, N>` for bitfield interop.
+macro_rules! impl_pfn_bounded {
+    ($bits:literal) => {
+        impl_frame_number_bounded!(Pfn, $bits);
+    };
+}
+
+use kernel::{
+    num::Bounded,
+    prelude::*, //
+};
+
+/// Physical Frame Number.
+///
+/// Represents a physical page in VRAM.
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub(crate) struct Pfn(u64);
+
+impl Pfn {
+    /// Create a new PFN from a frame number.
+    pub(crate) const fn new(frame_number: u64) -> Self {
+        Self(frame_number)
+    }
+
+    /// Get the raw frame number.
+    pub(crate) const fn raw(self) -> u64 {
+        self.0
+    }
+}
+
+impl From<u64> for Pfn {
+    fn from(val: u64) -> Self {
+        Self(val)
+    }
+}
+
+impl From<Pfn> for u64 {
+    fn from(pfn: Pfn) -> Self {
+        pfn.0
+    }
+}
+
+impl_pfn_bounded!(52);
-- 
2.34.1